Steam just changed its refund policy. If you buy a game on the Steam store, you have 14 days to decide if you want to get a refund for it, whatever the reason may be, but keep in mind that you’d also shouldn’t exceed two hours of play time to be eligible for a refund.
There’s also cases where you can get a refund for a piece of DLC, but not all kinds. The money that you’ll receive back will be put either on your Steam Wallet or directly back to service of which money was drawn from, but in some cases that won’t be possible so you’ll receive the refund in your Steam Wallet.
For more information about this new policy, go here.